Telecommunications systems are carrying increasing amounts of information, both in long distance networks as well as in metropolitan and local area networks. At present, data traffic is growing much faster than voice traffic, and includes high bandwidth video signals. In addition to the requirement for equipment to carry increasing amounts of telecommunication traffic there is a need to bring this information from the long distance networks to businesses and to locations where it can be distributed to residences over access networks.
The equipment, which has been developed to carry large amounts of telecommunication traffic, includes fiber optic transport equipment that can carry high-speed telecommunication traffic. The data rates on fiber optic systems can range from millions of bits per second (Mb/s) to billions of bits per second (Gb/s). In addition, multiple wavelengths of light can be carried on an optical fiber using Wavelength Division Multiplexing (WDM) techniques.
The ability to carry large amounts of telecommunication traffic on an optical fiber solves the long-distance point-to-point transport problem, but does not address the issue of how to add and remove traffic from the high-speed data stream. Equipment for adding and removing traffic has been developed and is referred to as “add-drop” multiplexers (ADMs).
Traditional designs for ADMs are based on the use of multiple interface cards which receive high-speed data streams, create a time division multiplex signal containing the multiple data streams, and route the time division multiplex signal to a cross-connect unit which can disassemble the data streams, remove or insert particular data streams, and send the signal to another interface card for transmission back into the networks. By aggregating the multiple data streams into a time division multiplexed data signal, the data rate of the time division multiplexed signal is by definition several times the rate of the maximum data rate supported by the interface cards. Traditional ADMs have proven adequate for interface data rates in the range of 155 Mb/s to 622 Mb/s.
However, optical signals of at least 2.4 Gb/s have become standard, and numerous problems arise with traditional ADMs due to the timing associated with the multiplexing and transmission of the high-speed signals between the interface cards and the cross-connect unit. Thus, there is a need for cross-connect equipment which can support multiple high-speed data streams (i.e., at least 2.4 Gb/s).
Standardized interfaces and transmission hierarchies for telecommunication signals have been developed and include Pleisochronous Digital Hierarchy (PDH), Synchronous Digital Hierarchy (SDH) standards, and Synchronous Optical Network (SONET). In addition to these telecommunication transport standards, standards have been developed for interconnecting businesses and computers within businesses. These Metropolitan and Local Area Network (MAN/LAN) standards include Ethernet, Gigabit Ethernet, Frame Relay, and Fiber Distributed Data Interface (FDDI). Other standards, such as Integrated Services Digital Network (ISDN) and Asynchronous Transfer Mode (ATM) have been developed for use at both levels.
Individual pieces of equipment can be purchased to support telecommunication or MAN/LAN standards. However, these devices generally either connect data streams using a single protocol or convert entire data streams from one protocol to another. Thus, there is a need for a device that can establish interconnectivity between interfaces at the MAN/LAN level, while providing cross-connection to interfaces at the telecommunication network level.
Multiple interfaces are presently supported in ADMs using different interface cards. High-speed interface cards must be inserted into particular slots in order to insure that the high-speed signals can be transported to and from the cross-connect unit and to and from the high-speed interface cards. It would be desirable to have a device in which all cards can support high-speed optical signals of at least 2.4 Gb/s, regardless of the card slot they are located in. Moreover, it would also be useful to have a device that would support routing, bridging, and concentration functions within MANs/LANs, as well as permitting access to telecommunication networks.
A data circuit is defined as all of the interface cards within a particular ADM that a particular data stream is transmitted to. If a particular interface card becomes inoperable, for example is removed, the data circuit becomes open. That is, the inoperable interface card prevents the data stream from being delivered to any interface card after the inoperable card. Thus, there is a need for a device that can reroute data streams within the data circuit when one or more of the interface cards forming the data circuit becomes inoperable.
For the foregoing reasons, there is a need for a flexible cross-connect apparatus that includes a data plane and can support multiple high-speed optical interfaces in any card slot. Furthermore, the flexible cross-connect apparatus should establish connectivity between data cards and the telecommunication networks. Moreover, the flexible cross-connect apparatus should be able to maintain a data circuit by rerouting data streams when one or more interface cards within the circuit becomes inoperable.